System for converting the number of lines of a television signal

ABSTRACT

A system for converting the number of lines of a television signal having interlaced frames each formed by signals of two adjacent fields, in which signals of each field of each frame are formed by sequentially weighting and combining line signals of the former and the latter of the two fields under the conditions that the order of lines is not reversed in the output frame and that the lines are not repeated in the same field.

This invention relates to a system for converting the number of lines inone field of a television signal having frames each formed by twoadjacent fields.

An object of this invention is to provide a system for converting thenumber of lines of one field of a television signal having frames eachformed by two adjacent fields, in which one field of an outputtelevision signal is formed by two interlaced successive fields, thatis, one frame of an input television signal.

The principle, construction and operation of this invention will beclearly understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIGS. 1A, 1B, 2A and 2B are line arrangement diagrams explanatory ofconventional line conversion,

FIGS. 3A and 3B are waveform diagrams showing waveform distortion causedby the conventional line conversion;

FIGS. 4A, 4B, 5A and 5B are line arrangement diagrams explanatory ofline conversion according to this invention;

FIGS. 6A and 6B are waveform diagrams showing waveform distortion causedby the line conversion of this invention;

FIG. 7 is a block diagram illustrating an example of this invention;

FIG. 8 is a time chart explanatory of waveforms in a 625/50 system;

FIG. 9 is a block diagram illustrating an example of a memory employedin the example shown in FIG. 7;

FIG. 10 is a line arrangement diagram explantory of line combiningaccording to this invention; and

FIG. 11 is a block diagram illustrating an example of a line combineremployed in the example shown in FIG. 7.

For ready understanding of the principle of the invention, a descriptionwill be given first of a conventional method for conversion of thenumber of lines from a television system adopted in Europe, i.e. a625/50 system, to that in the United States and in Japan, i.e. a 525/60system.

In case of decreasing the number of lines for conversion of the numberof lines in the prior art, as shown in FIG. 1A, only a required numberof those lines (for example, five lines indicated by solid lines) forforming one field of an output television signal, which are the closestto the lines of the output television signal, are extracted from lines(for example, six lines indicated by solid lines) of one field of aninput television signal, thereby to achieve conversion of the number oflines. Further, also in case of increasing the number of lines as shownin FIG. 1B, those of the lines (for example, five lines indicated bysolid lines) of one field of the input television signal, which are theclosest to the lines of the output television signal, are repeatedlyused as occasion demands, thus obtaining a required number of lines (forexample, six lines indicated by solid lines) for forming one field ofthe output television signal.

As a result of this, the straight lines a, b and c before conversionbecome such as identified by d, e and f to produce distortion as shownin FIG. 1B. To avoid this, there is employed a method such as is shownin FIGS. 2A and 2B in which two adjacent lines in the same field areweighted respectively and combined (numerical values indicating weightfactors to visually alleviate distortion). However, in a case where apicture signal, especially a picture signal S_(o) such as a white signalinclined by 45° to the scanning lines exists as shown in FIG. 3A (weightcombining ratio 2/4 : 2/4) or in FIG. 3B (weight combining ratio 1/4 :3/4), such a method is defective in that the signal waveform S_(o) afterconversion becomes remarkedly dull owing to a level change by the signalto produce greatly deteriorated resolution.

In accordance with this invention, the aforesaid defects can beeffectively eliminated as described below.

With the system of this invention, in case of decreasing the number oflines, as shown in FIG. 4A, those lines (for example, eleven linesindicated by solid and broken lines) of two interlaced successivefields, that is, one frame, of an input television signal which are theclosest to the lines (for example, five lines indicated by solid lines)of an output television signal, are extracted and sequentially selectedunder the conditions that the order of the lines in the output frame isnot reversed and that no repetition is effected in the same field, thusforming each output field. This apparently enables remarked alleviationof the distortion, as compared with the converted picture shown in FIGS.1A and 1B. Since the method for increasing the number of lines isapparent from FIG. 4B, no detailed description will be given. Namely, itis possible to obtain a converted signal without making its waveformdull and to reduce distortion of the picture.

In case of further reducing the distortion of the picture even ifresolution is a little lowered, it is possible to adopt such a method asis shown in FIGS. 5A and 5B, in which two adjacent lines in the sameframe are weighted respectively and combined as occasion demands. FIG.5A shows the case of converting the number of lines from 625 to 525 andFIG. 5B the case of converting the number of lines from 525 to 625. Alsoin this case, dullness of the waveform due to the above weight combiningis far smaller than that in FIGS. 3A and 3B as shown in FIGS. 6A and 6Bunder the same conditions. This naturally deteriorates resolution alittle as compared with that in the case of no weight combining oflines, but the amount of deterioration is negligibly small as comparedwith that in the prior art.

It is apparent that the above results are caused by an essentialdifference between signal processing in one field and that in one frame.Namely, as described previously, each complete picture of the televisionsignal is formed by one frame, that is, two successive fields, so thatthe formation of an output signal from one frame of an input signal isnothing but effective use of the amount of information twice as large asthat in the case of forming the output signal from one field of theinput signal. Consequently, deterioration of the quality of theconverted picture can easily be suppressed to substantially 1/2.

With reference to the drawings, an example of this invention will bedescribed as being applied to the conversion of the number of lines of atelevision signal of the 625/50 system to that of a television signal ofthe 525/60 system.

FIG. 7 is a fundamental system diagram for realizing the number-of-linesconversion system of this invention. Reference numeral 1 indicates asignal input terminal, 2 designates a memory; 3 represents a linecombiner; 4 denotes an address circuit (e.g. a non-locked control deviceof the kind shown in U.S. Pat. No. 3,676,585) for controlling theaddress-designation, the write operation and the read operation of thememory 2, 5 identifies a signal output terminal; 6 and 7 show inputterminals for horizontal and vertical synchronizing pulses of the 625/50system, respectively; and 8 and 9 refer to input terminals forhorizontal and vertical synchronizing pulses of the 525/60 system,respectively. The input television signal of the 625/50 system includesinformation of 625 lines in first and second fields, that is, in oneframe. Let it be assumed that this television signal is sampled, forexample, at 10 MHz, converted into an 80M-bit PCM code system, appliedas 8-bit parallel digital code words to the signal input terminal 1 andthen stored in the memory 2. Then, a signal of one field of the 525/60system is produced from the signal of one frame of the 625/50 systemstored in the memory 2. Since a field blanking period exists in 625lines of the input signal, there is no need of storing all the 625lines. In the present example, information of 588 lines except 37 linesof the field blanking period is stored. Namely, as illustrated in FIG.8, 18th to 311th lines in the first field and 331st to 624th lines inthe second field are sequentially stored in the memory 2 until theinstant of writing the next subsequent frame. Signals of 245 lines areproduced from the stored 588 lines by weight-combining signals of fivelines for each group of ten lines in twelve lines as will be describedlater, and a vertical blanking signal of the 525/60 system is added tothe above signals of produced 245 lines to provide an output signal.Thus, the output signal of 262.5 lines for one field is produced. Linesof the input signal are marked with numbers (H numbers) H₁ to H₂₉₄ andH₂₉₅ to H₅₈₈ for the address designation of the memory 2. Futher, inthis case, one line has information of 80M bit/sec. × 64μ sec. = 5125bits. However, these information bits are divided into groups of 8 bits(= 1 word) and marked with numbers (N numbers) N₁ to N₆₄₀ in the orderof arrangement of the words. At this time, it is also possible to storethe signal except the horizontal blanking period so as to reduce therequired capacity of the memory 2.

Each of the element circuits will hereinafter be described in detail.

The memory 2 comprises, as shown in FIG. 9, a write-in register 10, amemory matric plane 11, a read-out register 12 and a control circuit 13,and this memory 2 has a memory capacity of 588 × 640 = 376,320 words (1word = 8 bits) for storing the information of 588 lines. The addressesof the memory 2 are indicated by a combination (H_(i), N_(r)) using theaforementioned H numbers and N numbers, and the word information of eachaddress is identified by a combination W (H_(i), N_(r)), (i = 1, 2, . .. , 294, i + 294 = 295, 296, . . . , 588, r = 1, 2, . . . , 640).

The write-in register 10 sequentially stores therein the information of588 lines from (H₁, N₁) to (H₅₈₈, N₆₄₀) every word under control of thecontrol circuit 13 and holds the information until the next frame iswritten. The control circuit 13 comprises, as is well known for a memorymatrix, an address register, an address decoder, a word driver, atiming-and-control device, etc.

The read-out register 12 reads-out through a sense amplifier and dataselector (not shown), as is well known, information of two adjacentlines in one frame from the information of the stored first and secondfields under control of the control circuit 13 for effecting the aboveline combining, that is, weight combining as will be described later.Namely, the read-out register 12 supplies to the line combiner 3information of an address W(H_(i), N_(r)) of the first field andinformation of an address W (H_(i) ₊ 294, N_(r)) of the second field inthe 8-bit parallel form.

Thus, the write-in operation is achieved in the cycle of H_(a) = 64μ sfor one line and V_(a) = 20 ms for one field. The read-out operation isachieved in the cycle of H = 63.5μ s for one line and V = 16.7 ms forone field.

The line combiner 3 sequentially weights and combines the informationfrom the read-out register 12, that is, weight-combines adjacent linesof one frame every 10 lines to convert them into information of 5 lines,as shown in FIG. 10. In FIG. 10, solid-line arrows indicate the case offorming an odd-number field, and broken-line arrows indicate the case offorming an even-number field. FIG. 11 is a block diagram illustrating anexample of the line combiner 3. An input line 2a receives theinformation of the lines of the first field (the odd-number field), andan input line 2b receives the information of the lines of the secondfield (the even-number field). As described above, the line combiner 3combines the above information every 10 lines while changing weightfactors in such an order, for example, as shown in Table 1. The linecombiner 3 is composed of a scale-of-five counter 14 for obtaininginformation of 5 lines, 8-digit binary multipliers 15 and 16 whosemultiples are controlled by the above counter 14, an 8-digit binaryadder 17 and a field decision circuit 18 for detecting whether theodd-number field or the even-number field in response to verticalsynchronizing pulses to actuate the corresponding one group of differentmultiple groups of the multipliers 15 and 16. The field decision circuit18 comprises, for example, a cascade integrator circuit a disclosed in"Television Engineering", McGRAW-HILL BOOK COMPANY, Inc., 1952, pages205 to 206 to detect vertical synchronizing pulses, and a binary counterfor counting the detected vertical synchronizing pulses.

                  Table 1                                                         ______________________________________                                               Multiple                                                               State    Odd-number field                                                                              Even-number field                                    of       Multiplier                                                                              Multiplier                                                                              Multiplier                                                                            Multiplier                               Counter  15        16        15      16                                       ______________________________________                                        0        4/4       0         3/4     1/4                                      1        2/4       2/4       1/4     3/4                                      2        0         4/4       0       4/4                                      3        1/4       3/4       2/4     2/4                                      4        3/4       1/4       4/4     0                                        ______________________________________                                    

The line signal thus obtained is led to the signal output terminal 5.

Since conversion from 525 lines to 625 lines can be achieved bysubstantially the same element circuits and the same control system asthose in the system described above, detailed descriptions are omitted.

Although the foregoing description has been given in connection with thecase where the line information of the television signal to be convertedis digitalized and stored in the memory, it is a matter of course thatthe line information can be stored and processed as analog informationby the employment of charge coupled devices (CCD) or the like.

As has been described in the foregoing, the converted television signalof the present invention, is extremely improved in distortion of apicture and in deterioration of its waveform as compared with the signalobtainable with the conventional system. Therefore, the invention isapplicable not only to the signal conversion of commercial televisionsystems of different number of fields but also to the system conversionof picturephones of the same number of fields.

What we claim is:
 1. A system for converting the number of lines of aninput television signal having frames each formed by two adjacentinterlaced fields, comprising:input terminal means for receiving saidinput television signal; memory means connected to said input terminalmeans for successively storing said input television signal; firstsynchronizing terminal means for receiving horizontal synchronizingpulses and vertical synchronizing pulses of said input televisionsignal; second synchronizing terminal means for receiving horizontalsynchronizing pulses and vertical synchronizing pulses of an outputtelevision signal to be obtained; address circuit means connected tosaid memory means, said first synchronizing terminal means and saidsecond synchronizing terminal means for performing the write-inoperation to the memory means in response to said horizontalsynchronizing pulses and said vertical synchronizing pulses of the firstsynchronizing terminal means and for performing the read-out operationfrom the memory means in response to said horizontal synchronizingpulses and said vertical synchronizing pulses of said secondsynchronizing terminal means; line combiner means connected to saidmemory means and said second synchronizing terminal means for formingeach interlaced frame of said output television signal by signals of twoadjacent fields of said input television signal read-out from saidmemory means in response to said horizontal synchronizing pulses andsaid vertical synchronizing pulses of said second synchronizing terminalmeans under a condition where signals of each field of said each frameof said output television signal are formed by sequentially weightingand combining line signals of the former and the latter of the twofields of said input television signal so that the order of lines is notreversed in said output frame while the lines are not repeated in thesame field; and output terminal means connected to said line combinermeans for obtaining said output television signal.
 2. A system accordingto claim 1, in which said line combiner means comprises first multipliermeans connected to said memory means for multiplying the line signals ofan odd field of said input television signal readout from said memorymeans, second multiplier means connected to said memory means formultiplying the line signals of an even field of said input televisionsignal readout from the memory means, a scale-of-n counter meanscounting the horizontal synchronizing pulses of said secondsynchronizing terminal means after resetting by each of said verticalsynchronizing pulses of said second synchronizing terminal means forvarying the multiples of said first multiplier means and said secondmultiplier means in accordance with the states thereof, a decisioncircuit for detecting whether the odd number field or the even numberfield in response to the vertical synchronizing pulses of said secondsynchronizing terminal means to actuate corresponding one group ofdifferent multiple groups of the first multiplier means and the secondmultiplier means, and an adder means connected to the outputs of saidfirst multiplier means and the second multiplier means and the outputterminal means to provide an added output as said output televisionsignal at said output terminal means.